<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>demo</title>
  <script type="text/javascript" src="../vue.js"></script>
</head>

<body>
  <div id="app">
    <p>计数</p>
    <p> 年龄:{{person.age}}</p>
    <button @click="person.age++">++</button>
  </div>
</body>
<script type="text/javascript">
  Vue.config.productionTip = false;
  const vm = new Vue({
    el: "#app",
    data() {
      return {
        count: 0,
        person: {
          age: 18
        }
      }
    },
    watch: {
      person: {
        deep: true,
        handler() {
          alert("你老了")
        }
      }
    }
  })
</script>

</html>